The present application is a continuation of International Application PCT/SE2005/000423, filed Mar. 22, 2005, which claims priority to SE 0400773-8, filed Mar. 23, 2004, both of which are incorporated by reference.
The present invention relates to a method of producing lower emissions in the operation of a vehicle comprising an internal combustion engine which gives off exhaust gases to an exhaust system comprising a catalytic converter, injectors which are designed to inject hydrocarbon into the exhaust system or into the engine combustion chamber, and a transmission that can be driven by the engine.
The present invention also relates to an engine-driven vehicle comprising an internal combustion engine which in operation gives off exhaust gases to an exhaust system, comprising a catalytic converter, control elements, injectors, which are designed to inject hydrocarbon into the exhaust system or into the engine combustion chamber, and a transmission that can be driven by the engine.
The present invention also relates to a computer program for performing such a method on a computer.
In engine-driven vehicles catalytic converters of various types are nowadays used for exhaust emission control in order to achieve lower emissions. These catalytic converters are used in order to reduce to some extent the discharges of nitrogen compounds (NOx), for example. Due to various factors the catalytic converters may function less efficiently, the quantity of exhaust gases converted into nitrogen gas, carbon dioxide or water, for example, being reduced, which results in unnecessarily high exhaust emissions in the operation of said vehicles.
It is desirable to provide a method of cost-effectively achieving lower emissions from an engine-driven vehicle.
According to an aspect of the present invention, a method of the type specified in the introductory part includes selecting a gear in the vehicle's transmission as a function at least of information that catalytic conversion is required and information on the temperature in the exhaust system, so that the gear selected regulates the temperature in the exhaust system.
One advantage accruing from this solution is obtained through the use of synergetic effects of interaction between the transmission and the internal combustion engine, which in operation gives off exhaust gases to the exhaust casing. This advantage can be obtained by selecting the engine speed and the transmission gear when the vehicle is in operation in such a way that the rotational speed of the transmission output shaft is basically maintained whilst the engine speed is adjusted so that the exhaust gas temperature varies. This temperature adjustment in turn produces the lower exhaust emissions. This solution becomes very cost-effective, since according to the invention the vehicle does not need to be fitted with additional components. The method according to the invention means that the catalytic converter can be used for a longer period of time, since it is not exposed to such high stresses as previously, and in particular to high temperatures. With the method, exhaust emission control in motor vehicles can function better in practice. Since this gives the catalytic converter the advantage of a longer service life, it does not need to be removed from the vehicle for repair or replacement as often as hitherto, which means that the invention is both economic and time-saving, since the vehicle therefore does not need to be brought into a workshop as frequently.
A well-controlled temperature in the exhaust system minimizes the risk that the hydrocarbon used as reagent in various methods of reducing emissions will be destroyed by excessively high temperatures, for example, or become ineffective at excessively low temperatures. A further advantage of an aspect of the invention is that the risk of hydrocarbon escape (that is to say, non-reacting hydrocarbon) is reduced, especially in the case of transients, in that the temperature in the catalytic converter can be better controlled. Through improved control of the temperature in the catalytic converter the duty cycle of the catalytic converter can be increased. An aspect of the invention makes it possible to predict more accurately what will occur in the catalytic converter and in this way the thermal mass can be managed so that the reaction in the catalytic converter can be maintained for a longer period of time during a transient process.
According to one aspect of the invention lower emissions are achieved with the aid of a catalytic converter in a vehicle exhaust system. The catalytic converter may be of the LNC (Lean NOx Catalyst) type. By actively changing the gear on the vehicle driveline whilst maintaining the engine power output, even at low revolutions, it is possible to obtain an optimum temperature for an LNC catalyst. The optimum temperature may lie in a range in the order of 350° C. At an optimum catalytic converter temperature it is possible to achieve a more efficient catalysis between, for example, a hydrocarbon (HC compounds) injected into the exhaust system and NOx compounds, so that a larger quantity of nitrogen gas, carbon dioxide and water is formed in the catalytic converter. The nitrogen gas, the carbon dioxide and the water can then be expelled from the exhaust system. The method involves coordinated control of the engine and transmission.
With a temperature sensor a control unit can determine when it is time to improve the catalysis in the catalytic converter. In response to a signal, or from calculations, the control unit can temporarily deviate from stored gear selection strategies and any optimum fuel consumption in order to adjust the temperature in the vehicle exhaust system and hence also the temperature of a hydrocarbon injected into the exhaust system. For example, at a high engine output a control unit can actively switch to a temperature-limiting strategy. In concrete terms, this may mean downshifting gears in the transmission. At constant engine output, the temperature in the exhaust system falls as the engine speed increases. When the temperature in the exhaust system and hence also the substrate temperature has reached the required temperature, an ordinary gear selection strategy can be applied. The control unit is also designed to consider whether it is more advantageous to adjust the temperature at a later stage rather than on receipt of the initial signal.